/*
 * Copyright (c) 1994, 2013, Oracle and/or its affiliates. All rights reserved.
 * ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
 *
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 */

package java.lang;

import java.io.*;
import java.util.*;

/**
 * The {@code Throwable} class is the superclass of all errors and
 * exceptions in the Java language. Only objects that are instances of this
 * class (or one of its subclasses) are thrown by the Java Virtual Machine or
 * can be thrown by the Java {@code throw} statement. Similarly, only
 * this class or one of its subclasses can be the argument type in a
 * {@code catch} clause.
 *
 * For the purposes of compile-time checking of exceptions, {@code
 * Throwable} and any subclass of {@code Throwable} that is not also a
 * subclass of either {@link RuntimeException} or {@link Error} are
 * regarded as checked exceptions.
 *
 * <p>Instances of two subclasses, {@link java.lang.Error} and
 * {@link java.lang.Exception}, are conventionally used to indicate
 * that exceptional situations have occurred. Typically, these instances
 * are freshly created in the context of the exceptional situation so
 * as to include relevant information (such as stack trace data).
 *
 * <p>A throwable contains a snapshot of the execution stack of its
 * thread at the time it was created. It can also contain a message
 * string that gives more information about the error. Over time, a
 * throwable can {@linkplain Throwable#addSuppressed suppress} other
 * throwables from being propagated.  Finally, the throwable can also
 * contain a <i>cause</i>: another throwable that caused this
 * throwable to be constructed.  The recording of this causal information
 * is referred to as the <i>chained exception</i> facility, as the
 * cause can, itself, have a cause, and so on, leading to a "chain" of
 * exceptions, each caused by another.
 *
 * <p>One reason that a throwable may have a cause is that the class that
 * throws it is built atop a lower layered abstraction, and an operation on
 * the upper layer fails due to a failure in the lower layer.  It would be bad
 * design to let the throwable thrown by the lower layer propagate outward, as
 * it is generally unrelated to the abstraction provided by the upper layer.
 * Further, doing so would tie the API of the upper layer to the details of
 * its implementation, assuming the lower layer's exception was a checked
 * exception.  Throwing a "wrapped exception" (i.e., an exception containing a
 * cause) allows the upper layer to communicate the details of the failure to
 * its caller without incurring either of these shortcomings.  It preserves
 * the flexibility to change the implementation of the upper layer without
 * changing its API (in particular, the set of exceptions thrown by its
 * methods).
 *
 * <p>A second reason that a throwable may have a cause is that the method
 * that throws it must conform to a general-purpose interface that does not
 * permit the method to throw the cause directly.  For example, suppose
 * a persistent collection conforms to the {@link java.util.Collection
 * Collection} interface, and that its persistence is implemented atop
 * {@code java.io}.  Suppose the internals of the {@code add} method
 * can throw an {@link java.io.IOException IOException}.  The implementation
 * can communicate the details of the {@code IOException} to its caller
 * while conforming to the {@code Collection} interface by wrapping the
 * {@code IOException} in an appropriate unchecked exception.  (The
 * specification for the persistent collection should indicate that it is
 * capable of throwing such exceptions.)
 *
 * <p>A cause can be associated with a throwable in two ways: via a
 * constructor that takes the cause as an argument, or via the
 * {@link #initCause(Throwable)} method.  New throwable classes that
 * wish to allow causes to be associated with them should provide constructors
 * that take a cause and delegate (perhaps indirectly) to one of the
 * {@code Throwable} constructors that takes a cause.
 *
 * Because the {@code initCause} method is public, it allows a cause to be
 * associated with any throwable, even a "legacy throwable" whose
 * implementation predates the addition of the exception chaining mechanism to
 * {@code Throwable}.
 *
 * <p>By convention, class {@code Throwable} and its subclasses have two
 * constructors, one that takes no arguments and one that takes a
 * {@code String} argument that can be used to produce a detail message.
 * Further, those subclasses that might likely have a cause associated with
 * them should have two more constructors, one that takes a
 * {@code Throwable} (the cause), and one that takes a
 * {@code String} (the detail message) and a {@code Throwable} (the
 * cause).
 *
 * @author unascribed
 * @author Josh Bloch (Added exception chaining and programmatic access to stack trace in 1.4.)
 * @jls 11.2 Compile-Time Checking of Exceptions
 * @since JDK1.0
 */
public class Throwable implements Serializable {

  /**
   * use serialVersionUID from JDK 1.0.2 for interoperability
   */
  private static final long serialVersionUID = -3042686055658047285L;

  /**
   * Native code saves some indication of the stack backtrace in this slot.
   */
  private transient Object backtrace;

  /**
   * Specific details about the Throwable.  For example, for
   * {@code FileNotFoundException}, this contains the name of
   * the file that could not be found.
   *
   * @serial
   */
  private String detailMessage;


  /**
   * Holder class to defer initializing sentinel objects only used
   * for serialization.
   */
  private static class SentinelHolder {

    /**
     * {@linkplain #setStackTrace(StackTraceElement[]) Setting the
     * stack trace} to a one-element array containing this sentinel
     * value indicates future attempts to set the stack trace will be
     * ignored.  The sentinal is equal to the result of calling:<br>
     * {@code new StackTraceElement("", "", null, Integer.MIN_VALUE)}
     */
    public static final StackTraceElement STACK_TRACE_ELEMENT_SENTINEL =
        new StackTraceElement("", "", null, Integer.MIN_VALUE);

    /**
     * Sentinel value used in the serial form to indicate an immutable
     * stack trace.
     */
    public static final StackTraceElement[] STACK_TRACE_SENTINEL =
        new StackTraceElement[]{STACK_TRACE_ELEMENT_SENTINEL};
  }

  /**
   * A shared value for an empty stack.
   */
  private static final StackTraceElement[] UNASSIGNED_STACK = new StackTraceElement[0];

    /*
     * To allow Throwable objects to be made immutable and safely
     * reused by the JVM, such as OutOfMemoryErrors, fields of
     * Throwable that are writable in response to user actions, cause,
     * stackTrace, and suppressedExceptions obey the following
     * protocol:
     *
     * 1) The fields are initialized to a non-null sentinel value
     * which indicates the value has logically not been set.
     *
     * 2) Writing a null to the field indicates further writes
     * are forbidden
     *
     * 3) The sentinel value may be replaced with another non-null
     * value.
     *
     * For example, implementations of the HotSpot JVM have
     * preallocated OutOfMemoryError objects to provide for better
     * diagnosability of that situation.  These objects are created
     * without calling the constructor for that class and the fields
     * in question are initialized to null.  To support this
     * capability, any new fields added to Throwable that require
     * being initialized to a non-null value require a coordinated JVM
     * change.
     */

  /**
   * The throwable that caused this throwable to get thrown, or null if this
   * throwable was not caused by another throwable, or if the causative
   * throwable is unknown.  If this field is equal to this throwable itself,
   * it indicates that the cause of this throwable has not yet been
   * initialized.
   *
   * @serial
   * @since 1.4
   */
  private Throwable cause = this;

  /**
   * The stack trace, as returned by {@link #getStackTrace()}.
   *
   * The field is initialized to a zero-length array.  A {@code
   * null} value of this field indicates subsequent calls to {@link
   * #setStackTrace(StackTraceElement[])} and {@link
   * #fillInStackTrace()} will be be no-ops.
   *
   * @serial
   * @since 1.4
   */
  private StackTraceElement[] stackTrace = UNASSIGNED_STACK;

  // Setting this static field introduces an acceptable
  // initialization dependency on a few java.util classes.
  private static final List<Throwable> SUPPRESSED_SENTINEL =
      Collections.unmodifiableList(new ArrayList<Throwable>(0));

  /**
   * The list of suppressed exceptions, as returned by {@link
   * #getSuppressed()}.  The list is initialized to a zero-element
   * unmodifiable sentinel list.  When a serialized Throwable is
   * read in, if the {@code suppressedExceptions} field points to a
   * zero-element list, the field is reset to the sentinel value.
   *
   * @serial
   * @since 1.7
   */
  private List<Throwable> suppressedExceptions = SUPPRESSED_SENTINEL;

  /**
   * Message for trying to suppress a null exception.
   */
  private static final String NULL_CAUSE_MESSAGE = "Cannot suppress a null exception.";

  /**
   * Message for trying to suppress oneself.
   */
  private static final String SELF_SUPPRESSION_MESSAGE = "Self-suppression not permitted";

  /**
   * Caption  for labeling causative exception stack traces
   */
  private static final String CAUSE_CAPTION = "Caused by: ";

  /**
   * Caption for labeling suppressed exception stack traces
   */
  private static final String SUPPRESSED_CAPTION = "Suppressed: ";

  /**
   * Constructs a new throwable with {@code null} as its detail message.
   * The cause is not initialized, and may subsequently be initialized by a
   * call to {@link #initCause}.
   *
   * <p>The {@link #fillInStackTrace()} method is called to initialize
   * the stack trace data in the newly created throwable.
   */
  public Throwable() {
    fillInStackTrace();
  }

  /**
   * Constructs a new throwable with the specified detail message.  The
   * cause is not initialized, and may subsequently be initialized by
   * a call to {@link #initCause}.
   *
   * <p>The {@link #fillInStackTrace()} method is called to initialize
   * the stack trace data in the newly created throwable.
   *
   * @param message the detail message. The detail message is saved for later retrieval by the
   * {@link #getMessage()} method.
   */
  public Throwable(String message) {
    fillInStackTrace();
    detailMessage = message;
  }

  /**
   * Constructs a new throwable with the specified detail message and
   * cause.  <p>Note that the detail message associated with
   * {@code cause} is <i>not</i> automatically incorporated in
   * this throwable's detail message.
   *
   * <p>The {@link #fillInStackTrace()} method is called to initialize
   * the stack trace data in the newly created throwable.
   *
   * @param message the detail message (which is saved for later retrieval by the {@link
   * #getMessage()} method).
   * @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method).
   * (A {@code null} value is permitted, and indicates that the cause is nonexistent or unknown.)
   * @since 1.4
   */
  public Throwable(String message, Throwable cause) {
    fillInStackTrace();
    detailMessage = message;
    this.cause = cause;
  }

  /**
   * Constructs a new throwable with the specified cause and a detail
   * message of {@code (cause==null ? null : cause.toString())} (which
   * typically contains the class and detail message of {@code cause}).
   * This constructor is useful for throwables that are little more than
   * wrappers for other throwables (for example, {@link
   * java.security.PrivilegedActionException}).
   *
   * <p>The {@link #fillInStackTrace()} method is called to initialize
   * the stack trace data in the newly created throwable.
   *
   * @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method).
   * (A {@code null} value is permitted, and indicates that the cause is nonexistent or unknown.)
   * @since 1.4
   */
  public Throwable(Throwable cause) {
    fillInStackTrace();
    detailMessage = (cause == null ? null : cause.toString());
    this.cause = cause;
  }

  /**
   * Constructs a new throwable with the specified detail message,
   * cause, {@linkplain #addSuppressed suppression} enabled or
   * disabled, and writable stack trace enabled or disabled.  If
   * suppression is disabled, {@link #getSuppressed} for this object
   * will return a zero-length array and calls to {@link
   * #addSuppressed} that would otherwise append an exception to the
   * suppressed list will have no effect.  If the writable stack
   * trace is false, this constructor will not call {@link
   * #fillInStackTrace()}, a {@code null} will be written to the
   * {@code stackTrace} field, and subsequent calls to {@code
   * fillInStackTrace} and {@link
   * #setStackTrace(StackTraceElement[])} will not set the stack
   * trace.  If the writable stack trace is false, {@link
   * #getStackTrace} will return a zero length array.
   *
   * <p>Note that the other constructors of {@code Throwable} treat
   * suppression as being enabled and the stack trace as being
   * writable.  Subclasses of {@code Throwable} should document any
   * conditions under which suppression is disabled and document
   * conditions under which the stack trace is not writable.
   * Disabling of suppression should only occur in exceptional
   * circumstances where special requirements exist, such as a
   * virtual machine reusing exception objects under low-memory
   * situations.  Circumstances where a given exception object is
   * repeatedly caught and rethrown, such as to implement control
   * flow between two sub-systems, is another situation where
   * immutable throwable objects would be appropriate.
   *
   * @param message the detail message.
   * @param cause the cause.  (A {@code null} value is permitted, and indicates that the cause is
   * nonexistent or unknown.)
   * @param enableSuppression whether or not suppression is enabled or disabled
   * @param writableStackTrace whether or not the stack trace should be writable
   * @see OutOfMemoryError
   * @see NullPointerException
   * @see ArithmeticException
   * @since 1.7
   */
  protected Throwable(String message, Throwable cause,
      boolean enableSuppression,
      boolean writableStackTrace) {
    if (writableStackTrace) {
      fillInStackTrace();
    } else {
      stackTrace = null;
    }
    detailMessage = message;
    this.cause = cause;
    if (!enableSuppression) {
      suppressedExceptions = null;
    }
  }

  /**
   * Returns the detail message string of this throwable.
   *
   * @return the detail message string of this {@code Throwable} instance (which may be {@code
   * null}).
   */
  public String getMessage() {
    return detailMessage;
  }

  /**
   * Creates a localized description of this throwable.
   * Subclasses may override this method in order to produce a
   * locale-specific message.  For subclasses that do not override this
   * method, the default implementation returns the same result as
   * {@code getMessage()}.
   *
   * @return The localized description of this throwable.
   * @since JDK1.1
   */
  public String getLocalizedMessage() {
    return getMessage();
  }

  /**
   * Returns the cause of this throwable or {@code null} if the
   * cause is nonexistent or unknown.  (The cause is the throwable that
   * caused this throwable to get thrown.)
   *
   * <p>This implementation returns the cause that was supplied via one of
   * the constructors requiring a {@code Throwable}, or that was set after
   * creation with the {@link #initCause(Throwable)} method.  While it is
   * typically unnecessary to override this method, a subclass can override
   * it to return a cause set by some other means.  This is appropriate for
   * a "legacy chained throwable" that predates the addition of chained
   * exceptions to {@code Throwable}.  Note that it is <i>not</i>
   * necessary to override any of the {@code PrintStackTrace} methods,
   * all of which invoke the {@code getCause} method to determine the
   * cause of a throwable.
   *
   * @return the cause of this throwable or {@code null} if the cause is nonexistent or unknown.
   * @since 1.4
   */
  public synchronized Throwable getCause() {
    return (cause == this ? null : cause);
  }

  /**
   * Initializes the <i>cause</i> of this throwable to the specified value.
   * (The cause is the throwable that caused this throwable to get thrown.)
   *
   * <p>This method can be called at most once.  It is generally called from
   * within the constructor, or immediately after creating the
   * throwable.  If this throwable was created
   * with {@link #Throwable(Throwable)} or
   * {@link #Throwable(String, Throwable)}, this method cannot be called
   * even once.
   *
   * <p>An example of using this method on a legacy throwable type
   * without other support for setting the cause is:
   *
   * <pre>
   * try {
   *     lowLevelOp();
   * } catch (LowLevelException le) {
   *     throw (HighLevelException)
   *           new HighLevelException().initCause(le); // Legacy constructor
   * }
   * </pre>
   *
   * @param cause the cause (which is saved for later retrieval by the {@link #getCause()} method).
   * (A {@code null} value is permitted, and indicates that the cause is nonexistent or unknown.)
   * @return a reference to this {@code Throwable} instance.
   * @throws IllegalArgumentException if {@code cause} is this throwable.  (A throwable cannot be
   * its own cause.)
   * @throws IllegalStateException if this throwable was created with {@link #Throwable(Throwable)}
   * or {@link #Throwable(String, Throwable)}, or this method has already been called on this
   * throwable.
   * @since 1.4
   */
  public synchronized Throwable initCause(Throwable cause) {
    if (this.cause != this) {
      throw new IllegalStateException("Can't overwrite cause with " +
          Objects.toString(cause, "a null"), this);
    }
    if (cause == this) {
      throw new IllegalArgumentException("Self-causation not permitted", this);
    }
    this.cause = cause;
    return this;
  }

  /**
   * Returns a short description of this throwable.
   * The result is the concatenation of:
   * <ul>
   * <li> the {@linkplain Class#getName() name} of the class of this object
   * <li> ": " (a colon and a space)
   * <li> the result of invoking this object's {@link #getLocalizedMessage}
   * method
   * </ul>
   * If {@code getLocalizedMessage} returns {@code null}, then just
   * the class name is returned.
   *
   * @return a string representation of this throwable.
   */
  public String toString() {
    String s = getClass().getName();
    String message = getLocalizedMessage();
    return (message != null) ? (s + ": " + message) : s;
  }

  /**
   * Prints this throwable and its backtrace to the
   * standard error stream. This method prints a stack trace for this
   * {@code Throwable} object on the error output stream that is
   * the value of the field {@code System.err}. The first line of
   * output contains the result of the {@link #toString()} method for
   * this object.  Remaining lines represent data previously recorded by
   * the method {@link #fillInStackTrace()}. The format of this
   * information depends on the implementation, but the following
   * example may be regarded as typical:
   * <blockquote><pre>
   * java.lang.NullPointerException
   *         at MyClass.mash(MyClass.java:9)
   *         at MyClass.crunch(MyClass.java:6)
   *         at MyClass.main(MyClass.java:3)
   * </pre></blockquote>
   * This example was produced by running the program:
   * <pre>
   * class MyClass {
   *     public static void main(String[] args) {
   *         crunch(null);
   *     }
   *     static void crunch(int[] a) {
   *         mash(a);
   *     }
   *     static void mash(int[] b) {
   *         System.out.println(b[0]);
   *     }
   * }
   * </pre>
   * The backtrace for a throwable with an initialized, non-null cause
   * should generally include the backtrace for the cause.  The format
   * of this information depends on the implementation, but the following
   * example may be regarded as typical:
   * <pre>
   * HighLevelException: MidLevelException: LowLevelException
   *         at Junk.a(Junk.java:13)
   *         at Junk.main(Junk.java:4)
   * Caused by: MidLevelException: LowLevelException
   *         at Junk.c(Junk.java:23)
   *         at Junk.b(Junk.java:17)
   *         at Junk.a(Junk.java:11)
   *         ... 1 more
   * Caused by: LowLevelException
   *         at Junk.e(Junk.java:30)
   *         at Junk.d(Junk.java:27)
   *         at Junk.c(Junk.java:21)
   *         ... 3 more
   * </pre>
   * Note the presence of lines containing the characters {@code "..."}.
   * These lines indicate that the remainder of the stack trace for this
   * exception matches the indicated number of frames from the bottom of the
   * stack trace of the exception that was caused by this exception (the
   * "enclosing" exception).  This shorthand can greatly reduce the length
   * of the output in the common case where a wrapped exception is thrown
   * from same method as the "causative exception" is caught.  The above
   * example was produced by running the program:
   * <pre>
   * public class Junk {
   *     public static void main(String args[]) {
   *         try {
   *             a();
   *         } catch(HighLevelException e) {
   *             e.printStackTrace();
   *         }
   *     }
   *     static void a() throws HighLevelException {
   *         try {
   *             b();
   *         } catch(MidLevelException e) {
   *             throw new HighLevelException(e);
   *         }
   *     }
   *     static void b() throws MidLevelException {
   *         c();
   *     }
   *     static void c() throws MidLevelException {
   *         try {
   *             d();
   *         } catch(LowLevelException e) {
   *             throw new MidLevelException(e);
   *         }
   *     }
   *     static void d() throws LowLevelException {
   *        e();
   *     }
   *     static void e() throws LowLevelException {
   *         throw new LowLevelException();
   *     }
   * }
   *
   * class HighLevelException extends Exception {
   *     HighLevelException(Throwable cause) { super(cause); }
   * }
   *
   * class MidLevelException extends Exception {
   *     MidLevelException(Throwable cause)  { super(cause); }
   * }
   *
   * class LowLevelException extends Exception {
   * }
   * </pre>
   * As of release 7, the platform supports the notion of
   * <i>suppressed exceptions</i> (in conjunction with the {@code
   * try}-with-resources statement). Any exceptions that were
   * suppressed in order to deliver an exception are printed out
   * beneath the stack trace.  The format of this information
   * depends on the implementation, but the following example may be
   * regarded as typical:
   *
   * <pre>
   * Exception in thread "main" java.lang.Exception: Something happened
   *  at Foo.bar(Foo.java:10)
   *  at Foo.main(Foo.java:5)
   *  Suppressed: Resource$CloseFailException: Resource ID = 0
   *          at Resource.close(Resource.java:26)
   *          at Foo.bar(Foo.java:9)
   *          ... 1 more
   * </pre>
   * Note that the "... n more" notation is used on suppressed exceptions
   * just at it is used on causes. Unlike causes, suppressed exceptions are
   * indented beyond their "containing exceptions."
   *
   * <p>An exception can have both a cause and one or more suppressed
   * exceptions:
   * <pre>
   * Exception in thread "main" java.lang.Exception: Main block
   *  at Foo3.main(Foo3.java:7)
   *  Suppressed: Resource$CloseFailException: Resource ID = 2
   *          at Resource.close(Resource.java:26)
   *          at Foo3.main(Foo3.java:5)
   *  Suppressed: Resource$CloseFailException: Resource ID = 1
   *          at Resource.close(Resource.java:26)
   *          at Foo3.main(Foo3.java:5)
   * Caused by: java.lang.Exception: I did it
   *  at Foo3.main(Foo3.java:8)
   * </pre>
   * Likewise, a suppressed exception can have a cause:
   * <pre>
   * Exception in thread "main" java.lang.Exception: Main block
   *  at Foo4.main(Foo4.java:6)
   *  Suppressed: Resource2$CloseFailException: Resource ID = 1
   *          at Resource2.close(Resource2.java:20)
   *          at Foo4.main(Foo4.java:5)
   *  Caused by: java.lang.Exception: Rats, you caught me
   *          at Resource2$CloseFailException.&lt;init&gt;(Resource2.java:45)
   *          ... 2 more
   * </pre>
   */
  public void printStackTrace() {
    printStackTrace(System.err);
  }

  /**
   * Prints this throwable and its backtrace to the specified print stream.
   *
   * @param s {@code PrintStream} to use for output
   */
  public void printStackTrace(PrintStream s) {
    printStackTrace(new WrappedPrintStream(s));
  }

  private void printStackTrace(PrintStreamOrWriter s) {
    // Guard against malicious overrides of Throwable.equals by
    // using a Set with identity equality semantics.
    Set<Throwable> dejaVu =
        Collections.newSetFromMap(new IdentityHashMap<Throwable, Boolean>());
    dejaVu.add(this);

    synchronized (s.lock()) {
      // Print our stack trace
      s.println(this);
      StackTraceElement[] trace = getOurStackTrace();
      for (StackTraceElement traceElement : trace) {
        s.println("\tat " + traceElement);
      }

      // Print suppressed exceptions, if any
      for (Throwable se : getSuppressed()) {
        se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION, "\t", dejaVu);
      }

      // Print cause, if any
      Throwable ourCause = getCause();
      if (ourCause != null) {
        ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, "", dejaVu);
      }
    }
  }

  /**
   * Print our stack trace as an enclosed exception for the specified
   * stack trace.
   */
  private void printEnclosedStackTrace(PrintStreamOrWriter s,
      StackTraceElement[] enclosingTrace,
      String caption,
      String prefix,
      Set<Throwable> dejaVu) {
    assert Thread.holdsLock(s.lock());
    if (dejaVu.contains(this)) {
      s.println("\t[CIRCULAR REFERENCE:" + this + "]");
    } else {
      dejaVu.add(this);
      // Compute number of frames in common between this and enclosing trace
      StackTraceElement[] trace = getOurStackTrace();
      int m = trace.length - 1;
      int n = enclosingTrace.length - 1;
      while (m >= 0 && n >= 0 && trace[m].equals(enclosingTrace[n])) {
        m--;
        n--;
      }
      int framesInCommon = trace.length - 1 - m;

      // Print our stack trace
      s.println(prefix + caption + this);
      for (int i = 0; i <= m; i++) {
        s.println(prefix + "\tat " + trace[i]);
      }
      if (framesInCommon != 0) {
        s.println(prefix + "\t... " + framesInCommon + " more");
      }

      // Print suppressed exceptions, if any
      for (Throwable se : getSuppressed()) {
        se.printEnclosedStackTrace(s, trace, SUPPRESSED_CAPTION,
            prefix + "\t", dejaVu);
      }

      // Print cause, if any
      Throwable ourCause = getCause();
      if (ourCause != null) {
        ourCause.printEnclosedStackTrace(s, trace, CAUSE_CAPTION, prefix, dejaVu);
      }
    }
  }

  /**
   * Prints this throwable and its backtrace to the specified
   * print writer.
   *
   * @param s {@code PrintWriter} to use for output
   * @since JDK1.1
   */
  public void printStackTrace(PrintWriter s) {
    printStackTrace(new WrappedPrintWriter(s));
  }

  /**
   * Wrapper class for PrintStream and PrintWriter to enable a single
   * implementation of printStackTrace.
   */
  private abstract static class PrintStreamOrWriter {

    /**
     * Returns the object to be locked when using this StreamOrWriter
     */
    abstract Object lock();

    /**
     * Prints the specified string as a line on this StreamOrWriter
     */
    abstract void println(Object o);
  }

  private static class WrappedPrintStream extends PrintStreamOrWriter {

    private final PrintStream printStream;

    WrappedPrintStream(PrintStream printStream) {
      this.printStream = printStream;
    }

    Object lock() {
      return printStream;
    }

    void println(Object o) {
      printStream.println(o);
    }
  }

  private static class WrappedPrintWriter extends PrintStreamOrWriter {

    private final PrintWriter printWriter;

    WrappedPrintWriter(PrintWriter printWriter) {
      this.printWriter = printWriter;
    }

    Object lock() {
      return printWriter;
    }

    void println(Object o) {
      printWriter.println(o);
    }
  }

  /**
   * Fills in the execution stack trace. This method records within this
   * {@code Throwable} object information about the current state of
   * the stack frames for the current thread.
   *
   * <p>If the stack trace of this {@code Throwable} {@linkplain
   * Throwable#Throwable(String, Throwable, boolean, boolean) is not
   * writable}, calling this method has no effect.
   *
   * @return a reference to this {@code Throwable} instance.
   * @see java.lang.Throwable#printStackTrace()
   */
  public synchronized Throwable fillInStackTrace() {
    if (stackTrace != null ||
        backtrace != null /* Out of protocol state */) {
      fillInStackTrace(0);
      stackTrace = UNASSIGNED_STACK;
    }
    return this;
  }

  private native Throwable fillInStackTrace(int dummy);

  /**
   * Provides programmatic access to the stack trace information printed by
   * {@link #printStackTrace()}.  Returns an array of stack trace elements,
   * each representing one stack frame.  The zeroth element of the array
   * (assuming the array's length is non-zero) represents the top of the
   * stack, which is the last method invocation in the sequence.  Typically,
   * this is the point at which this throwable was created and thrown.
   * The last element of the array (assuming the array's length is non-zero)
   * represents the bottom of the stack, which is the first method invocation
   * in the sequence.
   *
   * <p>Some virtual machines may, under some circumstances, omit one
   * or more stack frames from the stack trace.  In the extreme case,
   * a virtual machine that has no stack trace information concerning
   * this throwable is permitted to return a zero-length array from this
   * method.  Generally speaking, the array returned by this method will
   * contain one element for every frame that would be printed by
   * {@code printStackTrace}.  Writes to the returned array do not
   * affect future calls to this method.
   *
   * @return an array of stack trace elements representing the stack trace pertaining to this
   * throwable.
   * @since 1.4
   */
  public StackTraceElement[] getStackTrace() {
    return getOurStackTrace().clone();
  }

  private synchronized StackTraceElement[] getOurStackTrace() {
    // Initialize stack trace field with information from
    // backtrace if this is the first call to this method
    if (stackTrace == UNASSIGNED_STACK ||
        (stackTrace == null && backtrace != null) /* Out of protocol state */) {
      int depth = getStackTraceDepth();
      stackTrace = new StackTraceElement[depth];
      for (int i = 0; i < depth; i++) {
        stackTrace[i] = getStackTraceElement(i);
      }
    } else if (stackTrace == null) {
      return UNASSIGNED_STACK;
    }
    return stackTrace;
  }

  /**
   * Sets the stack trace elements that will be returned by
   * {@link #getStackTrace()} and printed by {@link #printStackTrace()}
   * and related methods.
   *
   * This method, which is designed for use by RPC frameworks and other
   * advanced systems, allows the client to override the default
   * stack trace that is either generated by {@link #fillInStackTrace()}
   * when a throwable is constructed or deserialized when a throwable is
   * read from a serialization stream.
   *
   * <p>If the stack trace of this {@code Throwable} {@linkplain
   * Throwable#Throwable(String, Throwable, boolean, boolean) is not
   * writable}, calling this method has no effect other than
   * validating its argument.
   *
   * @param stackTrace the stack trace elements to be associated with this {@code Throwable}.  The
   * specified array is copied by this call; changes in the specified array after the method
   * invocation returns will have no affect on this {@code Throwable}'s stack trace.
   * @throws NullPointerException if {@code stackTrace} is {@code null} or if any of the elements of
   * {@code stackTrace} are {@code null}
   * @since 1.4
   */
  public void setStackTrace(StackTraceElement[] stackTrace) {
    // Validate argument
    StackTraceElement[] defensiveCopy = stackTrace.clone();
    for (int i = 0; i < defensiveCopy.length; i++) {
      if (defensiveCopy[i] == null) {
        throw new NullPointerException("stackTrace[" + i + "]");
      }
    }

    synchronized (this) {
      if (this.stackTrace == null && // Immutable stack
          backtrace == null) // Test for out of protocol state
      {
        return;
      }
      this.stackTrace = defensiveCopy;
    }
  }

  /**
   * Returns the number of elements in the stack trace (or 0 if the stack
   * trace is unavailable).
   *
   * package-protection for use by SharedSecrets.
   */
  native int getStackTraceDepth();

  /**
   * Returns the specified element of the stack trace.
   *
   * package-protection for use by SharedSecrets.
   *
   * @param index index of the element to return.
   * @throws IndexOutOfBoundsException if {@code index < 0 || index >= getStackTraceDepth() }
   */
  native StackTraceElement getStackTraceElement(int index);

  /**
   * Reads a {@code Throwable} from a stream, enforcing
   * well-formedness constraints on fields.  Null entries and
   * self-pointers are not allowed in the list of {@code
   * suppressedExceptions}.  Null entries are not allowed for stack
   * trace elements.  A null stack trace in the serial form results
   * in a zero-length stack element array. A single-element stack
   * trace whose entry is equal to {@code new StackTraceElement("",
   * "", null, Integer.MIN_VALUE)} results in a {@code null} {@code
   * stackTrace} field.
   *
   * Note that there are no constraints on the value the {@code
   * cause} field can hold; both {@code null} and {@code this} are
   * valid values for the field.
   */
  private void readObject(ObjectInputStream s)
      throws IOException, ClassNotFoundException {
    s.defaultReadObject();     // read in all fields
    if (suppressedExceptions != null) {
      List<Throwable> suppressed = null;
      if (suppressedExceptions.isEmpty()) {
        // Use the sentinel for a zero-length list
        suppressed = SUPPRESSED_SENTINEL;
      } else { // Copy Throwables to new list
        suppressed = new ArrayList<>(1);
        for (Throwable t : suppressedExceptions) {
          // Enforce constraints on suppressed exceptions in
          // case of corrupt or malicious stream.
          if (t == null) {
            throw new NullPointerException(NULL_CAUSE_MESSAGE);
          }
          if (t == this) {
            throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE);
          }
          suppressed.add(t);
        }
      }
      suppressedExceptions = suppressed;
    } // else a null suppressedExceptions field remains null

        /*
         * For zero-length stack traces, use a clone of
         * UNASSIGNED_STACK rather than UNASSIGNED_STACK itself to
         * allow identity comparison against UNASSIGNED_STACK in
         * getOurStackTrace.  The identity of UNASSIGNED_STACK in
         * stackTrace indicates to the getOurStackTrace method that
         * the stackTrace needs to be constructed from the information
         * in backtrace.
         */
    if (stackTrace != null) {
      if (stackTrace.length == 0) {
        stackTrace = UNASSIGNED_STACK.clone();
      } else if (stackTrace.length == 1 &&
          // Check for the marker of an immutable stack trace
          SentinelHolder.STACK_TRACE_ELEMENT_SENTINEL.equals(stackTrace[0])) {
        stackTrace = null;
      } else { // Verify stack trace elements are non-null.
        for (StackTraceElement ste : stackTrace) {
          if (ste == null) {
            throw new NullPointerException("null StackTraceElement in serial stream. ");
          }
        }
      }
    } else {
      // A null stackTrace field in the serial form can result
      // from an exception serialized without that field in
      // older JDK releases; treat such exceptions as having
      // empty stack traces.
      stackTrace = UNASSIGNED_STACK.clone();
    }
  }

  /**
   * Write a {@code Throwable} object to a stream.
   *
   * A {@code null} stack trace field is represented in the serial
   * form as a one-element array whose element is equal to {@code
   * new StackTraceElement("", "", null, Integer.MIN_VALUE)}.
   */
  private synchronized void writeObject(ObjectOutputStream s)
      throws IOException {
    // Ensure that the stackTrace field is initialized to a
    // non-null value, if appropriate.  As of JDK 7, a null stack
    // trace field is a valid value indicating the stack trace
    // should not be set.
    getOurStackTrace();

    StackTraceElement[] oldStackTrace = stackTrace;
    try {
      if (stackTrace == null) {
        stackTrace = SentinelHolder.STACK_TRACE_SENTINEL;
      }
      s.defaultWriteObject();
    } finally {
      stackTrace = oldStackTrace;
    }
  }

  /**
   * Appends the specified exception to the exceptions that were
   * suppressed in order to deliver this exception. This method is
   * thread-safe and typically called (automatically and implicitly)
   * by the {@code try}-with-resources statement.
   *
   * <p>The suppression behavior is enabled <em>unless</em> disabled
   * {@linkplain #Throwable(String, Throwable, boolean, boolean) via
   * a constructor}.  When suppression is disabled, this method does
   * nothing other than to validate its argument.
   *
   * <p>Note that when one exception {@linkplain
   * #initCause(Throwable) causes} another exception, the first
   * exception is usually caught and then the second exception is
   * thrown in response.  In other words, there is a causal
   * connection between the two exceptions.
   *
   * In contrast, there are situations where two independent
   * exceptions can be thrown in sibling code blocks, in particular
   * in the {@code try} block of a {@code try}-with-resources
   * statement and the compiler-generated {@code finally} block
   * which closes the resource.
   *
   * In these situations, only one of the thrown exceptions can be
   * propagated.  In the {@code try}-with-resources statement, when
   * there are two such exceptions, the exception originating from
   * the {@code try} block is propagated and the exception from the
   * {@code finally} block is added to the list of exceptions
   * suppressed by the exception from the {@code try} block.  As an
   * exception unwinds the stack, it can accumulate multiple
   * suppressed exceptions.
   *
   * <p>An exception may have suppressed exceptions while also being
   * caused by another exception.  Whether or not an exception has a
   * cause is semantically known at the time of its creation, unlike
   * whether or not an exception will suppress other exceptions
   * which is typically only determined after an exception is
   * thrown.
   *
   * <p>Note that programmer written code is also able to take
   * advantage of calling this method in situations where there are
   * multiple sibling exceptions and only one can be propagated.
   *
   * @param exception the exception to be added to the list of suppressed exceptions
   * @throws IllegalArgumentException if {@code exception} is this throwable; a throwable cannot
   * suppress itself.
   * @throws NullPointerException if {@code exception} is {@code null}
   * @since 1.7
   */
  public final synchronized void addSuppressed(Throwable exception) {
    if (exception == this) {
      throw new IllegalArgumentException(SELF_SUPPRESSION_MESSAGE, exception);
    }

    if (exception == null) {
      throw new NullPointerException(NULL_CAUSE_MESSAGE);
    }

    if (suppressedExceptions == null) // Suppressed exceptions not recorded
    {
      return;
    }

    if (suppressedExceptions == SUPPRESSED_SENTINEL) {
      suppressedExceptions = new ArrayList<>(1);
    }

    suppressedExceptions.add(exception);
  }

  private static final Throwable[] EMPTY_THROWABLE_ARRAY = new Throwable[0];

  /**
   * Returns an array containing all of the exceptions that were
   * suppressed, typically by the {@code try}-with-resources
   * statement, in order to deliver this exception.
   *
   * If no exceptions were suppressed or {@linkplain
   * #Throwable(String, Throwable, boolean, boolean) suppression is
   * disabled}, an empty array is returned.  This method is
   * thread-safe.  Writes to the returned array do not affect future
   * calls to this method.
   *
   * @return an array containing all of the exceptions that were suppressed to deliver this
   * exception.
   * @since 1.7
   */
  public final synchronized Throwable[] getSuppressed() {
    if (suppressedExceptions == SUPPRESSED_SENTINEL ||
        suppressedExceptions == null) {
      return EMPTY_THROWABLE_ARRAY;
    } else {
      return suppressedExceptions.toArray(EMPTY_THROWABLE_ARRAY);
    }
  }
}
